U.S. patent application number 10/353989 was filed with the patent office on 2003-09-25 for ceramic sintered body and process for producing the same.
This patent application is currently assigned to NGK SPARK PLUG CO., LTD.. Invention is credited to Mitsuoka, Takeshi, Miura, Eiji, Urashima, Kazuhiro, Yamamoto, Hiroshi.
Application Number | 20030181310 10/353989 |
Document ID | / |
Family ID | 27654484 |
Filed Date | 2003-09-25 |
United States Patent
Application |
20030181310 |
Kind Code |
A1 |
Yamamoto, Hiroshi ; et
al. |
September 25, 2003 |
Ceramic sintered body and process for producing the same
Abstract
A ceramic sintered body comprising from 90 to 99.8% by volume of
cordierite and from 0.2 to 10% by volume of mullite based on 100%
by weight of a total sum of the contents of the cordierite and the
mullite, and having a density of 2.48 g/cm.sup.3 or more.
Inventors: |
Yamamoto, Hiroshi;
(Kounan-shi, JP) ; Miura, Eiji; (Komaki-shi,
JP) ; Mitsuoka, Takeshi; (Kounan-shi, JP) ;
Urashima, Kazuhiro; (Kounan-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 Pennsylvania Avenue, NW
Washington
DC
20037-3213
US
|
Assignee: |
NGK SPARK PLUG CO., LTD.
|
Family ID: |
27654484 |
Appl. No.: |
10/353989 |
Filed: |
January 30, 2003 |
Current U.S.
Class: |
501/119 ;
501/122 |
Current CPC
Class: |
Y10T 279/11 20150115;
C04B 2235/3418 20130101; C04B 2235/5436 20130101; C04B 2235/3217
20130101; C04B 2235/77 20130101; C04B 35/195 20130101; C04B
2235/3206 20130101; C04B 2235/80 20130101; C04B 2235/3481 20130101;
H01L 21/6838 20130101; C04B 2235/3222 20130101; C04B 2235/3463
20130101; C04B 2235/9607 20130101; C04B 2235/36 20130101; H01L
21/6831 20130101; Y10T 279/23 20150115; C04B 2235/786 20130101 |
Class at
Publication: |
501/119 ;
501/122 |
International
Class: |
C04B 035/053; C04B
035/185; C04B 035/195 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2002 |
JP |
P.2002-024390 |
Claims
What is claimed is:
1. A ceramic sintered body comprising from 90 to 99.8% by volume of
cordierite and from 0.2 to 10% by volume of mullite based on 100%
by weight of a total sum of the contents of the cordierite and the
mullite, and having a density of 2.48 g/cm.sup.3 or more.
2. A ceramic sintered body comprising cordierite and mullite,
having a value of C, as defined by the following equation (1):
C=(A/B).times.100 (1) wherein, when measured by a X-ray
diffraction, A represents a peak intensity value of a (110) plane
of mullite crystal, and B represents a peak intensity value of a
(110) plane of cordierite crystal, of from 0.2 to 20, and having a
density of 2.48 g/cm.sup.3 or more.
3. The ceramic sintered body according to claim 1, wherein the
cordierite crystal has a mean particle size of 2 .mu.m or less.
4. The ceramic sintered body according to claim 2, wherein the
cordierite crystal has a mean particle size of 2 .mu.m or less.
5. The ceramic sintered body according to claim 1, which has a
thermal expansion coefficient, as measured at 20 to 25.degree. C.,
of from -0.2 to 0.2 ppm/K and a value, as obtained by dividing a
Young's modulus by the density, of 54.3 Gpa/g/cm.sup.3 or more.
6. The ceramic sintered body according to claim 2, which has a
thermal expansion coefficient, as measured at 20 to 25.degree. C.,
of from -0.2 to 0.2 ppm/K and a value, as obtained by dividing a
Young's modulus by the density, of 54.3 Gpa/g/cm.sup.3 or more.
7. A semi-conductor manufacture device comprising the ceramic
sintered body according to claim 1.
8. A semi-conductor manufacture device comprising the ceramic
sintered body according to claim 2.
9. A vacuum chuck comprising the ceramic sintered body according to
claim 1.
10. A vacuum chuck comprising the ceramic sintered body according
to claim 2.
11. An electrostatic chuck comprising the ceramic sintered body
according to claim 1.
12. An electrostatic chuck comprising the ceramic sintered body
according to claim 2.
13. A process for producing a ceramic sintered body, which
comprises: mixing at least one of a magnesium oxide powder and a
magnesium compound powder that becomes magnesium oxide upon
heating, at least one of an aluminum oxide powder and an aluminum
compound powder that becomes aluminum oxide upon heating, and at
least one of a silicon oxide powder and a silicon compound powder
that becomes silicon oxide upon heating; and sintering the mixture
so as to comprise from 90 to 99.8% by volume of cordierite and from
0.2 to 10% by volume of mullite based on 100% by weight of a total
sum of the contents of the cordierite and the mullite.
14. A process for producing a ceramic sintered body, which
comprises: mixing two or more of composite oxide powders of
magnesium, aluminum, and silicon; and sintering the mixture so as
to comprise from 90 to 99.8% by volume of cordierite and from 0.2
to 10% by volume of mullite based on 100% by weight of a total sum
of the contents of the cordierite and the mullite.
15. A process for producing a ceramic sintered body, which
comprises: mixing at least one of a magnesium oxide powder, a
magnesium compound powder that becomes magnesium oxide upon
heating, an aluminum oxide powder, an aluminum compound powder that
becomes aluminum oxide upon heating, a silicon oxide powder and a
silicon compound powder that becomes silicon oxide upon heating,
and at least one of composite oxide powders of magnesium, aluminum
and silicon; and sintering the mixture so as to comprise from 90 to
99.8% by volume of cordierite and from 0.2 to 10% by volume of
mullite based on 100% by weight of a total sum of the contents of
the cordierite and the mullite.
16. The process according to claim 13, wherein the powders have a
mean particle size of 2.0 .mu.m or less.
17. The process according to claim 14, wherein the powders have a
mean particle size of 2.0 .mu.m or less.
18. The process according to claim 15, wherein the powders have a
mean particle size of 2.0 .mu.m or less.
19. The process according to claim 13, wherein the sintering is
carried out at from 1,300 to 1,450.degree. C. for from 1 to 5
hours.
20. The process according to claim 14, wherein the sintering is
carried out at from 1,300 to 1,450.degree. C. for from 1 to 5
hours.
21. The process according to claim 15, wherein the sintering is
carried out at from 1,300 to 1,450.degree. C. for from 1 to 5
hours.
Description
FIELD OF THE INVENTION
[0001] The present invention relates a ceramic sintered body and a
process of producing the same. More specifically, the invention
relates to a ceramic sintered body comprising cordierite having a
specified amount of mullite dispersed therein, the mullite being
low in thermal expansion and having a large value obtained by
dividing a Young's modulus by a density (hereinafter referred to
"specific rigidity"), and to a process of producing the same.
[0002] The invention is utilized for, for example, ceramic parts
for semi-conductor manufacture devices, ceramic parts for precision
control machines, ceramic parts for optical instruments, and
catalyst carriers.
BACKGROUND OF THE INVENTION
[0003] Hitherto, as low thermal expansion ceramic sintered bodies
are known aluminum titanate, lithium alumino-silicate-based
ceramics such as eucryptite, .beta.-spondumene, and petalite, and
magnesium alumino-silicate-based ceramics such as cordierite.
[0004] Though the aluminum titanate and the lithium
alumino-silicate-based ceramics have a small thermal expansion
coefficient, they have a small Young's modulus so that they are
liable to deform by an external force or gravity. Accordingly,
their application to precision machine parts or optical instrument
parts in which dimensional changes or shape changes are
disliked.
[0005] On the other hand, the cordierite has hitherto been applied
as a low thermal expansion ceramic sintered body to filters,
honeycombs, and refractories. However, this is a porous body, and
its Young's modulus is low as from about 70 to 90 Gpa. Further, its
thermal expansion coefficient is about 0.5 ppm/K, and it cannot be
said that this value is sufficiently small.
[0006] Hitherto, in order to obtain a minute cordierite having a
small thermal coefficient, there is known a method for making a
petalite phase or a .beta.-spodumene phase coexistent (see
JP-A-11-209171 (the term "JP-A" as used herein means an "unexamined
published Japanese patent application")). However, according to
this method, cordierite sintered bodies having a sufficiently small
thermal coefficient are not obtained. Further, there is known a
technology in which a rare earth element is added in order to
obtain a cordierite sintered body having a small porosity and a
small thermal expansion coefficient (see JP-A-10-53460). However,
even in this case, it cannot be said that the thermal expansion
coefficient is sufficiently small.
SUMMARY OF THE INVENTION
[0007] The invention is to solve the foregoing problems of the
related art and is aimed to provide a ceramic sintered body that is
low in thermal expansion and has a high specific rigidity and a
process of producing the same.
[0008] In one aspect, the ceramic sintered body according to the
invention comprises from 90 to 99.8% by volume of cordierite and
from 0.2 to 10% by volume of mullite based on 100% by weight of the
total sum of the contents of the cordierite and the mullite, and
having a density of 2.48 g/cm.sup.3 or more.
[0009] In another aspect, the ceramic sintered body according to
the invention comprises cordierite and mullite, has a value of C,
as defined by the following equation (1):
C=(A/B).times.100 (1)
[0010] wherein, when measured by the X-ray diffraction, A
represents a peak intensity value of the (110) plane of mullite
crystal, and B represents a peak intensity value of the (110) plane
of cordierite crystal, of from 0.2 to 20 (the value C being
hereinafter referred to as "peak intensity ratio"), and has a
density of 2.48 g/cm.sup.3 or more.
[0011] According to the both aspects, the invention can provide a
ceramic sintered body having a mean particle size of cordierite
crystal of 2 .mu.m or less.
[0012] In addition, the invention can provide a ceramic sintered
body has a thermal expansion coefficient, as measured at 20 to
25.degree. C., of from -0.2 to 0.2 ppm/K and a specific rigidity of
54.3 Gpa/g/cm.sup.3 or more.
[0013] The ceramic sintered body according to the invention can
suitably be used as a member for semi-conductor manufacture
device.
[0014] The ceramic sintered body according to the invention can
suitably be used as a member for vacuum chuck (constituted of a
ceramic sintered body).
[0015] The ceramic sintered body according to the invention can
suitably be used as a member for electrostatic chuck (constituted
of a ceramic sintered body).
[0016] The process of producing a ceramic sintered body according
to the invention comprises (1) mixing at least one of a magnesium
oxide powder and a magnesium compound powder that becomes magnesium
oxide upon heating, at least one of an aluminum oxide powder and an
aluminum compound powder that becomes aluminum oxide upon heating,
and at least one of a silicon oxide powder and a silicon compound
powder that becomes silicon oxide upon heating; (2) mixing two or
more of composite oxide powders of magnesium, aluminum, and
silicon; or (3) mixing at least one of the respective metal oxide
powders and the respective metal compound powders and at least one
of the metal composite oxide powders, and sintering the mixture so
as to comprise from 90 to 99.8% by volume of cordierite and from
0.2 to 10% by volume of mullite based on 100% by weight of the
total sum of the contents of the cordierite and the mullite.
[0017] According to this production process, it is possible to
provide a ceramic sintered body having a thermal expansion
coefficient, as measured at 20 to 25.degree. C., of from -0.2 to
0.2 ppm/K and a specific rigidity of 54.3 Gpa/g/cm.sup.3 or
more.
[0018] Incidentally, in the invention, the case where the thermal
expansion coefficient is less than 0 ppm/K means that the sintered
body thermally shrinks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] [FIG. 1]
[0020] A graph showing the relationship between the amount of
mullite as contained and the thermal expansion coefficient and the
specific rigidity value.
[0021] [FIG. 2]
[0022] A chart of the X-ray diffraction of the ceramic sintered
body of Example 3.
[0023] [FIG. 3]
[0024] A perspective view to show a partially broken section of a
semi-conductor wafer and a vacuum chuck constituted of a ceramic
sintered body.
[0025] [FIG. 4]
[0026] A perspective view to show a partially broken section of an
electrostatic chuck device constituted of an electrostatic chuck
and a base plate.
1 [Description of Reference Numerals and Signs] 1: Vacuum chuck
(adsorbing plate) 3, 35: Semi-conductor wafer 5: Substrate 7:
Adsorbing hole 9: Projection 11: Sealing section 21: Electrostatic
chuck 27: Base plate 31, 33: Internal electrode 29: Electrostatic
chuck device
DETAILED DESCRIPTION OF THE INVENTION
[0027] The invention will be described below in detail.
[0028] In one aspect, the ceramic sintered body according to the
invention comprises from 90 to 99.8% by volume of cordierite
(2MgO.2Al.sub.2O3.5SiO.sub.2) and from 0.2 to 10% by volume of
mullite (3Al.sub.2O3.2SiO.sub.2) based on 100% by weight of the
total sum of the contents of the cordierite and the mullite. The
content of the cordierite is from 90 to 99.8% by volume, preferably
from 92 to 99.5% by volume, more preferably from 95 to 99.3% by
volume, and most preferably from 95 to 99.2% by volume. When the
content of cordierite is less than 90% by volume, though the
specific rigidity is large, the thermal expansion coefficient is
also large, and hence, such is not preferred. On the other hand,
when it exceeds 99.8% by volume, since a spinel phase or a glass
phase having a large thermal expansion coefficient, or a
cristobalite phase having a small Young's modulus deposits, the
thermal expansion coefficient becomes large, and the specific
rigidity becomes small, and hence, such is not preferred, too.
[0029] The term "% by volume" as referred to herein means % by
volume of each of cordierite and mullite formed by the reaction of
the raw material powders during sintering based on 100% by weight
of the total sum of the cordierite and the mullite.
[0030] The content of the mullite is from 0.2 to 10% by volume,
preferably from 0.5 to 8% by volume, more preferably from 0.7 to 5%
by volume, and most preferably from 0.8 to 5% by volume. When the
content of the mullite is less than 0.2% by volume, since a spinel
phase or a glass phase having a large thermal expansion
coefficient, or a cristobalite phase having a small Young's modulus
deposits, the thermal expansion coefficient becomes large, and the
specific rigidity becomes small, and hence, such is not preferred.
On the other hand, when it exceeds 10% by weight, though the
specific rigidity is large, the thermal expansion coefficient is
also large, and hence, such is not preferred, too. Further,
preferably, in this sintered body, the crystal phase as detected by
the X-ray diffraction measurement consists only of a cordierite
phase and a mullite phase.
[0031] Incidentally, the sintered body can contain trace amounts of
other components (inevitable impurities on the manufacture, and
other components) than the cordierite and the mullite, unless the
density, the thermal expansion coefficient, and the specific
rigidity are influenced.
[0032] In another aspect, the ceramic sintered body according to
the invention comprises cordierite and mullite and has a peak
intensity ratio of from 0.2 to 20, preferably from 0.5 to 16, more
preferably from 0.7 to 10, and most preferably from 0.8 to 10. When
the peak intensity ratio of the ceramic sintered body is less than
0.2, since a spinel phase or a glass phase having a large thermal
expansion coefficient, or a cristobalite phase having a small
Young's modulus deposits, the thermal expansion coefficient becomes
large, and the specific rigidity becomes small, and hence, such is
not preferred. On the other hand, when it exceeds 20, though the
specific rigidity is large, the thermal expansion coefficient is
also large, and hence, such is not preferred, too. Further,
preferably, in this sintered body, the crystal phase as detected by
the X-ray diffraction measurement consists only of a cordierite
phase and a mullite phase.
[0033] Incidentally, the sintered body can contain trace amounts of
other components (inevitable impurities on the manufacture, and
other components) than the cordierite and the mullite, unless the
density, the thermal expansion coefficient, and the specific
rigidity are influenced.
[0034] In the both aspects of the invention, the ceramic sintered
body has a density of 2.48 g/cm.sup.3 or more, preferably 2.49
g/cm.sup.3 or more, and more preferably 2.50 g/cm.sup.3 or more.
When the density of the ceramic sintered body is less than 2.48
g/cm.sup.3, a large Young's modulus is not obtained, and the
specific rigidity is small, and hence, such is not preferred.
Further, since the number of pores increases, when the surface of
the ceramic sintered body is polished, surface smoothness is hardly
obtained.
[0035] The cordierite crystal contained in the ceramic sintered
body preferably has a mean particle size of 2 .mu.m or less, more
preferably 1.9 .mu.m or less, and most preferably 1.8 .mu.m or
less. Since in the cordierite crystal, the thermal expansion
coefficient on the a axis differs from that on the c axis, when the
mean particle size of the cordierite crystal exceeds 2 .mu.m, micro
cracks are generated by the difference in the thermal expansion in
the sintered body during the sintering step, and the specific
rigidity of the resulting ceramic becomes small, and hence, such is
not preferred.
[0036] The ceramic sintered body preferably has a thermal expansion
coefficient, as measured at 20 to 25.degree. C., of from -0.2 to
0.2 ppm/K, more preferably from -0.16 to 0.16 ppm/K, further
preferably from -0.11 to 0.11 ppm/K, and most preferably from -0.08
to 0.08 ppm/K. Further, the ceramic sintered body preferably has a
specific rigidity of 54.3 GPg/g/cm.sup.3 or more, more preferably
54.6 GPg/g/cm.sup.3 or more, further preferably 54.8 GPg/g/cm.sup.3
or more, and most preferably 54.9 GPg/g/cm.sup.3 or more. Among
them, it is preferable that not only the thermal expansion
coefficient is from -0.2 to 0.2 ppm/K, but also the specific
rigidity is 54.3 GPg/g/cm.sup.3 or more; it is more preferable that
not only the thermal expansion coefficient is from -0.16 to 0.16
ppm/K, but also the specific rigidity is 54.6 GPg/g/cm.sup.3 or
more; it is further preferable that not only the thermal expansion
coefficient is from -0.11 to 0.11 ppm/K, but also the specific
rigidity is 54.8 GPg/g/cm.sup.3 or more; and it is most preferable
that not only the thermal expansion coefficient is from -0.08 to
0.08 ppm/K, but also the specific rigidity is 54.9 GPg/g/cm.sup.3
or more.
[0037] Further, with respect to the thermal expansion coefficient
and the specific rigidity, as shown in FIG. 1, the following
embodiments (1) to (4) are preferred depending upon the content of
the mullite.
[0038] (1) In the case where the content of the mullite is from 0.2
to 10% by volume, not only the thermal expansion coefficient is
from -0.03 to 0.20 ppm/K, but also the specific rigidity is from
54.4 to 56.6 Gpa/g/cm.sup.3.
[0039] (2) In the case where the content of the mullite is from 0.5
to 8% by volume, not only the thermal expansion coefficient is from
-0.03 to 0.16 ppm/K, but also the specific rigidity is from 54.7 to
56.5 Gpa/g/cm.sup.3.
[0040] (3) In the case where the content of the mullite is from 0.7
to 5% by volume, not only the thermal expansion coefficient is from
-0.03 to 0.08 ppm/K, but also the specific rigidity is from 54.9 to
56.0 Gpa/g/cm.sup.3.
[0041] (4) In the case where the content of the mullite is from 0.8
to 5% by volume, not only the thermal expansion coefficient is from
-0.03 to 0.08 ppm/K, but also the specific rigidity is from 55.0 to
56.0 Gpa/g/cm.sup.3.
[0042] Next, the process of producing a ceramic sintered body
according to the invention will be described below.
[0043] In the production process of the invention, at least one of
a magnesium oxide powder and a magnesium compound powder that
becomes magnesium oxide upon heating, at least one of an aluminum
oxide powder and an aluminum compound powder that becomes aluminum
oxide upon heating, and at least one of a silicon oxide powder and
a silicon compound powder that becomes silicon oxide upon heating
may be mixed and used. Each of these compounds is only required to
become an oxide upon heating. As such compounds are enumerated a
carbonate, a hydrogencarbonate, a hydroxide, and a nitrate of each
of the metals. Further, besides the respective metal oxide powders
and the respective metal compound powders, two or more of composite
oxide powders of the foregoing metals (i.e., magnesium, aluminum,
and silicon) may be mixed and used. As the composite oxide powders
are enumerated powders of, e.g., cordierite, mullite, and other
aluminosilicates. Moreover, at least one of the respective metal
oxide powders and the respective metal compound powders and at
least one of the metal composite oxide powders may be mixed and
used. For example, one or more of powders of, e.g., cordierite,
mullite, and other aluminosilicates and one or more of powders of,
e.g., magnesia, magnesium carbonate, alumina, aluminum hydroxide,
and silica can be used. Also, calcined powders can be used as the
raw material powders.
[0044] Each of the foregoing powders preferably has a mean particle
size of 2.0 .mu.m or less, more preferably 1.9 .mu.m or less, and
most preferably 1.8 .mu.m or less. When the particle size of the
powder exceeds 2.0 .mu.m, a sintered body having a large Young's
modulus is not obtained, and the specific rigidity is small, and
hence, such is not preferred. The metal oxide powders are weighed
and mixed such that these powders are reacted with each other
during sintering to give a sintered body comprising from 90 to
99.8% by volume of a cordierite phase and from 0.2 to 10% by volume
of a mullite phase. Preferably, in this sintered body, the crystal
phase as detected by the X-ray diffraction measurement consists
only of the cordierite phase and the mullite phase. Incidentally,
trace amounts of other raw materials (inevitable impurities on the
manufacture, and other raw materials), which will constitute other
phases than the cordierite phase and the mullite phase, may be
mixed, unless the density, the thermal expansion coefficient, and
the specific rigidity are influenced.
[0045] Thereafter, the mixture may be molded. There are no
particular limitations with respect to the shape and size of the
molding. Further, there are no particular limitations with respect
to the molding method.
[0046] Subsequently, the molding is sintered to obtain a ceramic
sintered body. The sintering is carried out preferably at from
1,300 to 1,450.degree. C. for from 1 to 5 hours in a prescribed
atmosphere. Further, the sintering atmosphere is not limited, but
the sintering is preferably carried out in air. However, the
sintering may be carried out in an inert gas atmosphere such as
argon or in vacuo, or in a non-oxidative atmosphere such as
nitrogen gas. In addition, while the sintered body is preferably
obtained by sintering under atmospheric pressure, in order to
obtain a more minute sintered body, the sintered body after the
sintering under atmospheric pressure may be further subjected to an
HIP (hot isotactic pressing) processing. Moreover, sintering under
pressure, such as HP (hot press), may be employed.
[0047] To the ceramic sintered body as produced by this production
process can be applied the foregoing thermal expansion coefficient
and specific rigidity.
[0048] The ceramic sintered body according to the invention can be
used as a member for semi-conductor manufacture device.
[0049] This enumerates one of utilities of the ceramic sintered
body according to the invention.
[0050] Accordingly, when the ceramic sintered body of the invention
is employed as a member of a semi-conductor manufacture device to
be used for the manufacture of, for example, semi-conductor wafers,
the deformation of the device by heat can be controlled so that a
semi-conductor wafer having superior dimensional precision can be
obtained.
[0051] The ceramic sintered body according to the invention can be
used as a member for vacuum chuck.
[0052] This enumerates one of utilities of the ceramic sintered
body according to the invention.
[0053] Accordingly, when the ceramic sintered body of the invention
is employed as a member of a vacuum chuck to be used for the
manufacture of, for example, semi-conductor wafers, the deformation
of the member by heat can be controlled so that a semi-conductor
wafer having superior dimensional precision can be obtained.
[0054] The ceramic sintered body according to the invention can be
used as a member for electrostatic chuck.
[0055] The foregoing ceramic sintered body can also be applied to
electrostatic chucks (for example, in the case where a wafer is
held by using a Coulomb force).
EXAMPLES
[0056] The invention will be specifically described below with
reference to the Examples.
[0057] [1] Preparation of Ceramic Sintered Body:
[0058] A commercially available cordierite powder was mixed with
predetermined amounts of a magnesia powder, a silica powder, an
alumina powder and a mullite powder so as to have a composition as
shown in Table 1, and the mixture was wet pulverized in the
presence of water as a solvent by using high-purity alumina flint
pebbles (purity: 99.9% or more). After the pulverization, the
powder had a mean particle size of 1.7 .mu.m. Thereafter, a binder
was added to the powder, and the mixture was spray dried. Next, the
resulting mixture was molded into a predetermined shape and
sintered. For all of the samples, the sintering was carried out in
air under atmospheric pressure at a sintering temperature of from
1,300 to 1,450.degree. C. for a holding time of 2 hours. There were
thus obtained samples of Examples 1 to 5 and Comparative Examples 1
to 3.
[0059] Table 2 shows the amount of cordierite and the amount of
mullite contained in each sample, and the sintering temperature,
the density, the peak intensity ratio, the Young's modulus, the
specific rigidity value, and the thermal expansion coefficient of
each sample. Further, FIG. 1 shows the relationship between the
amount of mullite and the thermal expansion coefficient and the
specific rigidity in each of Examples 1 to 5 and Comparative
Examples 1 to 3.
[0060] Incidentally, in Table 2, the term "% by volume" means % by
volume of each of cordierite and mullite formed by the reaction of
the raw material powders based on 100% by weight of the total sum
of the cordierite and the mullite.
2TABLE 1 Amount of Amount of cordierite magnesia Amount of Amount
of Amount of powder powder alumina powder silica powder mullite
powder Sample (% by weight) (% by weight) (% by weight) (% by
weight) (% by weight) Example 1 92.8 2.10 0 5.13 0 Example 2 94.5
1.61 0 3.92 0 Example3 100 0 0 0 0 Example 4 97.5 0 0 0 2.50
Example 5 97.5 0 1.79 0.71 0 Example 6 93.8 0 0 0 6.24 Comparative
89.5 3.04 0 7.43 0 Example 1 Comparative 87.7 0 0 0 12.3 Example 2
Comparative 100 0 0 0 0 Example 3
[0061]
3TABLE 2 Amount Amount of of Thermal cordierite mullite Sintering
Peak Young's Specific expansion (% by (% by temperature Density
intensity modulus rigidity coefficient Sample volume) volume)
(.degree. C.) (g/cm.sup.3) ratio (Gpa) (Gpa/g/cm.sup.3) (ppm/K)
Example 1 99 1 1,400 2.50 1 138 55.2 0.02 Example 2 98.5 1.5 1,400
2.50 3 139 55.6 -0.03 Example 3 97 3 1,400 2.51 6 140 55.8 0.02
Example 4 95 5 1,400 2.52 10 141 56.0 0.08 Example 5 94.5 5.5 1,400
2.52 11 141 56.0 0.10 Example 6 92 8 1,400 2.53 16 143 56.5 0.16
Comparative 100 0 1,400 2.49 0 135 54.2 0.22 Example 1 Comparative
87 13 1,450 2.56 30 145 56.6 0.48 Example 2 Comparative 97 3 1,350
2.37 6 120 50.6 0.06 Example 3
[0062] [2] Evaluation of Physical Properties, Etc.:
[0063] The evaluation of the Examples and Comparative Examples as
shown in Table 2 was made in the following manner.
[0064] (1) Mean Particle Size of Powder:
[0065] The particle size distribution was measured by the laser
scatter method, and its 50% diameter was designated as the mean
particle size.
[0066] (2) Contents of Cordierite and Mullite:
[0067] The sintered body was measured by the X-ray diffraction, and
the amount of mullite was calculated by a calibration curve
previously prepared from the peak intensity of the (110) plane of
mullite crystal and the (110) plane of cordierite crystal. The
calibration curve was prepared by preparing sintered bodies of
cordierite to which mullite had been added in an amount of 0%, 5%
and 10% by volume, respectively, and measuring these sintered
bodies by the X-ray diffraction to determine a ratio of the peak
intensity of the (110) plane of mullite crystal and the (110) plane
of cordierite crystal.
[0068] (3) Peak Intensity Ratio:
[0069] The sintered body was measured by the X-ray diffraction, and
the peak intensity ratio was determined from the peak intensity of
the (110) plane of the resulting cordierite crystal and the peak
intensity of the (110) plane of the resulting mullite crystal
according to the foregoing equation
[0070] (1) (see the X-ray diffraction chart of the ceramic sintered
body of Example 3 as shown in FIG. 2).
[0071] (4) Density of Sintered Body:
[0072] The evaluation was made by the Archimedes' method as defined
in JIS R 1634, and the numerical value was rounded off to the
second decimal place according to JIS Z 8401.
[0073] (5) Mean Particle Size of Cordierite Particles in Sintered
Body:
[0074] The sintered body was mirror finished and thermally etched,
and then observed by SEM (scanning electron microscope) . The mean
particle size was calculated from the SEM photograph by the
intercept technique. The cordierite particles of each of the
samples of the Examples and Comparative Examples had a mean
particle size of 1.8 .mu.m.
[0075] (6) Thermal Expansion Coefficient:
[0076] The evaluation was made by the laser interferometry as
defined in JIS R 3251, thereby calculating a mean thermal expansion
coefficient at 20 to 25.degree. C.
[0077] (7) Specific Rigidity:
[0078] The specific rigidity was calculated by dividing the value
of the Young's modulus by the density.
[0079] Further, the Young's modulus was measured at room
temperature by the ultrasonic pulse technique as defined in JIS R
1602.
[0080] [3] Effects of the Examples:
[0081] As shown in FIG. 1 and Table 2, in Comparative Example 1
(ceramic sintered body consisting only of cordierite, which is free
from mullite) and Comparative Example 2 (ceramic sintered body
consisting of 87% by volume of cordierite and 13% by volume of
mullite), the thermal expansion coefficient is large as 0.22 ppm/K
and 0.48 ppm/K, respectively. In particular, in Comparative Example
2, the thermal expansion coefficient is very large. Further, the
specific rigidity is 54.2 Gpa/g/cm.sup.3 and 56.6 Gpa/g/cm.sup.3,
respectively, and especially, it can be understood that in
Comparative Example 1, the specific rigidity is small. In addition,
according to Table 2, in Comparative Example 3 (ceramic sintered
body consisting of 97% by volume of cordierite and 3% by volume of
mullite and having a small density as 2.37 g/cm.sup.3), though the
thermal expansion coefficient is small as 0.06 ppm/K, the specific
rigidity is very small as 50.6 Gpa/g/cm.sup.3.
[0082] In contrast, as shown in FIG. 1 and Table 2, in Examples 1
to 6, the thermal expansion coefficient is small as from -0.03 to
0.16 ppm/K. Especially, in Examples 1 to 5, the thermal expansion
coefficient is small as from -0.03 to 0.10 ppm/K, the values of
which are very small as from about {fraction (1/10)} to 1/3 of that
in Comparative Example 1. In particular, in Examples 1 and 3, the
thermal expansion coefficient is extremely small as about {fraction
(1/10)} of that in Comparative Example 1. That is, in Example 1 (a
small amount (1% by volume) of mullite is added to cordierite) and
Example 3 (a small amount (3% by volume) of mullite is added to
cordierite), the thermal expansion coefficient is abruptly small as
0.02 ppm/K as compared with that (0.22 ppm/K) of Comparative
Example 1.
[0083] In addition, in Examples 1 to 6, the specific rigidity is
large as from 55.2 to 56.5 Gpa/g/cm.sup.3 as compared with that in
Comparative Example 1.
[0084] In the light of the above, it can be understood that the
ceramic sintered bodies of Examples 1 to 5 have a superior thermal
expansion coefficient and a specific rigidity and are quite
superior in balance between the both. Further, as shown in FIG. 1,
the thermal expansion coefficient is approximately curved having a
downward convex shape, and exhibits an unexpected behavior.
[0085] The Examples give rise to unexpected effects from the
related art such that the thermal expansion coefficient is small,
and the specific rigidity is large, as compared with the
conventionally known cordierite. It may be considered that these
effects are brought by the following reasons. That is, the
formation region of the cordierite is very narrow, and even a
little deviation in the composition results in deposition of a
second phase. Accordingly, when the composition of the cordierite
sintered body is deviated a little to the mullite formation side,
the deposition of a phase having a small Young's modulus and a
large thermal expansion coefficient is controlled so that it
becomes possible to stably produce a sintered body having a small
thermal expansion coefficient and a large Young's modulus.
Incidentally, even when it is intended to form a single phase of
cordierite, a glass phase and the like are inevitably formed, so
that the single phase of cordierite cannot be stably formed, and
the thermal expansion coefficient becomes large.
[0086] [4] Applications of the Examples:
[0087] Since the ceramic sintered body according to the invention
contains cordierite having a low thermal expansion coefficient as
the major component, the thermal expansion coefficient of the whole
of the ceramic sintered body is extremely low, and the dimensional
change and the shape change with the temperature change are little.
Moreover, by sintering the materials constituting the ceramic
sintered body, it is possible to obtain a ceramic sintered body
having not only a high density but also a high specific
rigidity.
[0088] Accordingly, by using the ceramic sintered body according to
the invention, there gives rise to a marked effect for enabling to
provide ceramic parts that are little in the dimensional change and
the shape change with the temperature change and high in the
rigidity, such as ceramic parts that can be suitably used for, for
example, semi-conductor manufacture devices, precision control
machines, optical instruments, and catalyst carriers.
[0089] Next, the utilities of the ceramic member comprising the
ceramic sintered body according to the invention will be described
below.
[0090] (1) First, a vacuum chuck using the ceramic sintered body
having the constitution of the foregoing Examples and a
semi-conductor manufacture device using the vacuum chuck will be
shown.
[0091] As shown in FIG. 3, a vacuum chuck 1 is a disc-like
adsorbing plate that adsorbs a semi-conductor wafer 3 by a suction
force by the reduced pressure and holds it.
[0092] The vacuum chuck 1 is provided with a disc-like substrate 5,
adsorbing holes 7 penetrating through the substrate 5 in the
thickness direction (for reducing the pressure), a number of
projections 9 protruding to the side of an adsorbing surface K of
the substrate 5 (the side of the semi-conductor wafer 3), and a
sealing section 11 protruding such that it circularly encircles the
surrounding of the projections 9.
[0093] The vacuum chuck 1 is installed in a well-known polishing
machine (not shown) constituting a part of the semi-conductor
device and used. The polishing machine is a CMP (chemical
mechanical polishing) device for undergoing CMP against the
semi-conductor wafer 3 and is mainly configured of a rotatably
aligned platen and a polishing head aligned at the upper side of
the platen as a vacuum suction device.
[0094] In the polishing machine, the vacuum chuck 1 is installed in
the polishing head, and a vacuum pump is actuated to reduce the air
pressure of a vacuum space within the polishing head. Thus, a
difference in the air pressure inside and outside the adsorbing
holes 7 of the vacuum chuck 1 is generated, thereby adsorbing the
semi-conductor wafer 3 onto adsorbing surface K of the vacuum chuck
1.
[0095] Next, in a state where the semi-conductor wafer 3 is
disposed between a polishing pad of the platen and the vacuum chuck
1, a slurry for CMP is fed to the surface of the polishing pad, and
the platen and the polishing head are rotated to undergo polishing
of the surface of the semi-conductor wafer 3.
[0096] As described above, since the vacuum chuck 1 is constituted
of the ceramic sintered body having the forgoing properties, has
low thermal expansion properties and a high rigidity, and is little
in the dimensional change and the shape change with the temperature
change, it can produce the semi-conductor wafer 3 having high
dimensional precision.
[0097] (2) Next, an electrostatic chuck using the ceramic sintered
body having the constitution of the foregoing Examples as another
application will be described.
[0098] As shown in FIG. 4, an electrostatic chuck 21 contains a
disc-like member comprising the foregoing ceramic sintered body as
a substrate 23, and a metal-made disc-like base plate 27 is welded
to one surface of the electrostatic chuck 21 (the back surface in
the lower portion of FIG. 4) via a welding layer 25. Incidentally,
the assembly comprising the electrostatic chuck 21 having the base
plate 27 welded thereto is called an electrostatic chuck device
29.
[0099] A pair of internal electrodes 31, 33 are embedded inside the
electrostatic chuck 21 (i.e., inside the substrate 23). The other
surface of the electrostatic chuck 21 (the front surface in the
upper portion of FIG. 4) constitutes an adsorbing surface (chuck
surface) 37 for, for example, adsorbing and fixing a semi-conductor
wafer 35 thereto.
[0100] Incidentally, through-holes (not shown) may be provided such
that they penetrate through the electrostatic chuck 21 and the base
plate 27 in the vertical direction in FIG. 4, through which are fed
an He gas for cooling at the side of the chuck surface 37.
[0101] A direct-current voltage of about .+-.1,000 V is applied to
the electrostatic chuck 21 to generate a Coulomb force for
adsorbing the semi-conductor wafer 35, and using this adsorbing
force, the semi-conductor wafer 35 is adsorbed and fixed.
[0102] As described above, since the electrostatic chuck 21 is
constituted of the ceramic sintered body having the forgoing
properties and is little in the dimensional change and the shape
change with the temperature change, it can produce the
semi-conductor wafer 35 having high dimensional precision.
[0103] In the light of the above, as compared with the
cordierite-based ceramics of the related art, the ceramic sintered
body according to the invention has a small thermal expansion
coefficient and has a large specific rigidity, while keeping a good
balance between the both. Accordingly, the ceramic sintered body
according to the invention can be suitably utilized for parts of
precision control machines and parts of optical instruments that
are required to have low thermal expansion properties and a high
specific rigidity, or parts that are required to have high
resistance to thermal shock.
[0104] In addition, according to the production process of the
invention, ceramic sintered bodies having a small thermal expansion
coefficient and a large specific rigidity can be easily
produced.
[0105] This application is based on Japanese Patent application JP
2002-24390, filed Jan. 31, 2002, the entire content of which is
hereby incorporated by reference, the same as if set forth at
length.
* * * * *